Dialysis: Dangerous X-ray views

20. April 2011

For thousands of dialysis patients, the news comes as a shock: the radiation exposure from CT or X-rays is supposed to increase the risk of cancer.

Among the reports in last weeks Journal of the American Society Nephrology (JASN), the publication slightly foundered. And yet the reading is worthwhile even in retrospect. Because if one believes the painstakingly gathered facts, dialysis patients show a cancer rate up to 1.5 times higher than people without the same therapy. The significantly higher probability of getting cancer while receiving dialysis, according to the medical profession, has a simple explanation: many have to undergo X-ray treatment repeatedly over the years. Still, the broad view among radiologists in the clinic seems not to have changed, as the Italian medical team under Marco Brambilla of the University Hospital “Maggiore della Carità” Novara, has now established.

For three years, the scientists observed a representatively selected group of 106 dialysis patients, and calculated the radiation exposure of the subjects on the basis of hospital records. Summary of the study: in total, computed tomography was used 248 times, with radiologists searching mostly for causes of neurological, respiratory or hemorrhagic complications. 1300 radiological examinations took place during the observation period as a whole, seen statistically every dialysis patient was X-rayed 4.3 times.

About 76 percent of the recorded amount of radiation came from investigations using computed tomography (CT), while conventional X-rays contributed nineteen percent of the overall exposure. Only 22 of the 106 study participants were exposed to doses of less than 3 mSv (millisievert), for more than a third of all participants the total load was, with well over 50 mSv, clearly too high. 16 percent of the total group had even received radiation doses of 100 mSv per year, which is associated with a significant increase in risk for cancer deaths. The physicians estimated the accumulated radiation doses and rely on and made reference to statistic knowledge gained with survivors of the atomic bomb explosion in Hiroshima. It was shown there that cumulative doses of radiation of 100 mSv per year pose a huge risk.

Doctors David Pickens and Martin Sandler of the American Vanderbilt School of Medicine see the problem in the too-rapid use of X-rays on dialysis patients. “Certain methods are often used, because a large amount of information comes to be available in a short time,” she criticises in an accompanying article in the journal the Problem with CT & Co.

For the American Society of Nephrology (ASN), founded in 1966, the Italian findings are important evidence for the adjustment of “real day-to-day dealing with X-ray operation in the clinic – but also without X-ray-exposure, patients with kidney diseases seem to especially strongly subject to cancer. According to co-author Andreana De Mauri, mechanisms not yet understood trigger higher cancer rates. For example, a kidney transplant results in a five-fold higher probability of a cancer – why this is so nobody until now has been able to explain. Too much X-ray radiation, fear the authors of the study, possibly reinforces this trend.

The Italian researchers are, with their criticism directed at the hasty use of harmful methods, not alone. In Germany, the Federal Office for Radiation Protection (BfS) in July 2010 criticised the fact that “in Germany by international comparison too much X-raying is done,” and “direct-dose intensive examinations such as computed tomography have increased greatly in recent years. The goal is to reduce the load to the necessary minimum.“

In fact, the BfS introduced in August 2003 so-called diagnostic reference values, ie. DRLs, which were updated last summer. Thus, the new diagnostic reference value for an X-ray of the pelvis is 40 per cent lower than the old value. The main point to highlight here is that the radiation risk from X-ray declines by the same percentage. This demonstrated “the expected trend towards a reduction of radiation exposure with regard to each individual investigation.” What was also new was the introduction of reference values for four types of CT examination in children.

Particularly alarming, observed the team under Brambilla on a less positive note, was one aspect of the treatment given to dialysis patients: young people who are waiting for a transplant are particularly strongly exposed to X-rays. Cumulative doses of 60 mSv or more in each individual organ in this case seem to be normal consequence of the X-ray examinations. By comparison, the effective dose resulting from medical treatments given to non-dialysis patients amounts to, on average, 1.9 mSv per year.